Connected: An Internet Encyclopedia
The `in-addr.arpa` Domain

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### The `in-addr.arpa` Domain

DNS has a few special cases you need to be aware of. Probably the most important of these is the `in-addr.arpa` domain, which is used to convert 32-bit numeric IP addresses back into domain names. This is used, for example, by Internet web servers, which receive connections from IP addresses and wish to obtain domain names to record in log files. Remember that IP addresses are written as four decimal numbers (one for each byte), seperated by periods.

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Connected: An Internet Encyclopedia
The `in-addr.arpa` Domain